Field of the Invention
The present invention relates to trochoid pumps, and more particularly, to noise control measures for them, and concerned with an effective one for use as a fuel pump for an automotive vehicle, for example.
2. Related Art Statement
As a trochoid pump for use as a fuel pump for an automotive vehicle, in Japanese Patent Laid-Open No. 60-156988, there has been described one comprising: an outer gear rotor and an inner gear rotor which are different in number of teeth from each other; pressure chambers defined by the distances of teeth of both rotors and an end plate, whose volumes are increased or decreased in accordance with rotations of both rotors; an intake opening communicated with the pressure chambers whose volumes are gradually increasing; and an outlet opening communicated with the pressure chambers whose volumes are gradually decreasing; wherein, in accordance with the rotations of both rotors, fuel is taken into the respective pressure chambers through the intake opening and fed under pressure through the outlet opening.
However, in the conventional trochoid pump of the type described, even in a minimum gap position between the teeth of both rotors, i.e. a so-called dead portion (a volume portion not contributing to the discharge), pressure from the discharge side is transmitted through a tip clearance between both rotors, whereby positive pressure is resulted, so that a large change in chamber pressure occurs when both rotors are turned from the dead portion to the intake side, thus resulting in occurrence of noises.